1. Field of the Invention
The invention relates to a powder spray-coating cabin. More particularly, the present invention relates to a powder spray-coating cabin fitted with two mutually opposite object wall-passages used in the transportation of objects to be coated through the cabin and with a suction channeling system configured at a lower end of an inside cabin space used to aspirate air and excess powder out of the inside cabin space.
2. Description of the Related Art
A powder spray-coating cabin of this kind is known from EP 0 839 583 A2. It may be a vertically cylindrical cabin fitted with a funnelling floor and communicating at the cabin center through a vacuum hookup with an external suction source. A similar cylindrical powder spray-coating cabin is known from DE 195 00 782 A1. In addition to the cabin floor in the form of an evacuation funnel, this latter design also includes a gutter-like floor rim along the cabin wall allowing evacuating, besides the flow from the said funnel, also air and powder particles, from the cabin. The German patent document DE 198 37 877 A1 discloses a vertically cylindrical cabin fitted with a planar floor plate. A diametrical slot runs through the floor plate allowing displacing powder particles on the floor through a rotating cleaning device.
Conventionally, spray-coating powders are fed pneumatically to spray implements, the so-called spray guns, which in turn spray these powders pneumatically and with electrostatic assistance onto the objects to be sprayed. A slight pressure deficit is maintained in the spray-coating cabins during the spray-coating process to prevent powder particles escaping from said cabin to the outside and furthermore for the purpose of evacuating excess powder (recoiling from the object or sprayed past it). Excess powder is evacuated to prevent excessively high concentrations that might entail powder-dust explosions, and also for purposes of recovery and recycling. The larger the objects to be coated, the larger also the volumetric flow of exhaust air to be removed from the inside of the cabin. This volumetric flow is generated by a suction source (blower) which is connected to the evacuation duct. The volumetric flow of exhaust air consists of the air of the pneumatically supplied powder and of the air which is aspirated through cabin apertures, in particular through the wall apertures passing the objects in the cabin wall, and of excess powder.
The objective of the invention is to increase the rate of powder spray-coating especially as regards large objects while circumventing disadvantageous flows of air or powder inside the cabin. Moreover the invention aims to improve coating quality and coating efficiency. The design of the invention shall be simple and economical and allow quickly passing to another kind of powder.
This problem is solved by the features of claim 1.
The invention offers the further substantial advantage that the cabin floor no longer need be a deep funnel and that the system of the evacuation channel below the cabin floor also may be made substantially more shallow and accordingly the cabin sub-structures no longer require an excavated pit and the powder spray-coating cabin can be erected without such a pit while the inside cabin space remains at the same height as in the state of the art.
The invention is especially advantageous when applied to vertically cylindrical cabins, though it is also appropriate for such coating cabins of which the horizontal cross-section is square or rectangular, oval or the like. The expression xe2x80x9cvertically cylindricalxe2x80x9d denotes that the cabin""s coating space assumes the shape of a vertical cylinder. Preferably this cylinder shall be cross-sectionally circular in the horizontal, though it may also assumes other shapes such as an arcuate or polygonal contour. However corner-subtending cross-sections entail more difficulties in cleaning than do arcuate or circular ones and also may generate disadvantageous air flows.